JP2022157587A - Manufacturing method for flux-cored cut wire and weld joint - Google Patents

Abstract

To provide a manufacturing method for a flux-cored cut wire and a weld joint which can suppress the generation of low-temperature cracks without carrying out base metal preheating work and form a weld metal having a favorite bead shape.SOLUTION: This invention includes a gas-shield arc-welding flux-cored wire comprising a steel jacket with a Ni content of 50 mass % or less and flux charging the interior of the steel jacket, containing in a sum total of 0.01%-20.00% of rare earth oxide by mass% to the total mass of the flux-cored wire, and having a Cr content of less than 0-22.00 mass% by mass% to the total mass of the flux-cored wire in a chemical composition excluding fluoride, nitride, oxide, and metal carbonate.SELECTED DRAWING: None

Description

The present disclosure relates to flux-cored wires for gas-shielded arc welding and methods of making welded joints.

In recent years, there has been an increasing demand for larger and lighter construction and industrial machinery, and along with this, ultra-high-strength steel sheets such as 780 MPa grade steel and 980 MPa grade steel have come to be used. there is The reasons why these ultra-high-strength steel sheets are used are because the weight of the product can be reduced, the amount of steel used can be reduced, which reduces the cost of steel and transportation, and the thinness of the steel reduces the weight of the steel. This is because it is easy to handle and the amount of welding is reduced, so it is expected to shorten the manufacturing period and reduce the construction cost.

For example, in Patent Document 1, in a Ni-based alloy flux-cored wire having a Ni-based alloy as the outer sheath, the filling rate of the contained flux is 10 to 33% by weight with respect to the total weight of the wire, and the flux composition is , TiO ₂ : 2 to 10 wt%, SiO ₂ : 0.1 to 3 wt%, Al ₂ O ₃ : 0.01 to 2 wt%, ZrO ₂ : 0.4 to 3 wt%, Li, At least one selected from the group consisting of Na and K compounds: 0.01 to 0.4% by weight in terms of total amount of Li, Na and K, metal component: 1 to 25% by weight in total amount, slag component: total amount Ni-based alloy flux-cored wires are described which are characterized by containing 4 to 15 wt.
It is described that the Ni-based alloy flux-cored wire of Patent Document 1 has excellent welding workability, few weld defects, and excellent hot crack resistance in MAG welding of Ni-containing steel and Ni-based alloy. there is

Further, Patent Document 2 discloses a Ni-based alloy flux-cored wire having a Ni-based alloy containing Nb and/or Mn as the outer sheath, wherein the filling rate of the included flux is 15 to 36% by weight with respect to the total weight of the wire. Yes, and the flux composition is TiO ₂ : 2 to 10 wt%, SiO ₂ : 0.1 to 3 wt%, ZrO ₂ : 0.4 to 4 wt%, Li, Na and K compounds relative to the total weight of the wire. At least one selected from the group consisting of: 0.01 to 0.4% by weight in terms of Li, Na, and K equivalents; metal components: 1 to 25% by weight in total; slag components: 4 to 15 in total. % by weight and is substantially free of Al ₂ O ₃ , carbonates, Fe oxides and Mn oxides.
The Ni-based alloy flux-cored wire of Patent Document 2 does not cause slag seizure in welding Ni steel or Ni-based alloys, has excellent hot cracking resistance, and is excellent in welding workability in all positions and in bead shape. Something is stated.

In addition, flux-cored wires are also disclosed in Patent Documents 3 to 9.

JP-A-2000-117488 JP-A-2000-343276 WO2019/102932 JP 2011-125875 A WO2017/188275 Japanese translation of PCT publication No. 2016-515942 JP-A-61-169196 WO2017/154725 JP-A-06-106382

For example, in welding high-strength extra-thick steel plates, preheating is performed to suppress cold cracking. In order to suppress the occurrence of cold cracking and to omit or simplify the preheating work, it is effective to reduce the amount of diffusible hydrogen during welding. In order to reduce the amount of diffusible hydrogen, an invention has been reported in which the flux and welding wire contain fluoride. This mechanism is thought to be due to the fact that the fluoride in the welding material is separated by the arc, the hydrogen partial pressure in the arc atmosphere is lowered by the fluorine material, and the amount of hydrogen dissolved in the molten pool is reduced. However, if fluoride is contained, the molten pool tends to drip, and welding workability (especially vertical weldability) is lowered. In addition, high-strength steel sheets are sometimes required to have high-temperature cracking resistance.
The flux-cored wires disclosed in Patent Documents 1 to 9 have room for further improvement in terms of improving welding workability and suppressing hot cracking of weld metal in gas-shielded arc welding.

An object of the present disclosure is to provide a flux-cored wire and a method for manufacturing a welded joint, in which welding workability is high and hot cracking of the weld metal is suppressed in gas-shielded arc welding.

The gist of the present disclosure is as follows.
<1> A flux-cored wire for gas-shielded arc welding, comprising a steel sheath having a Ni content of 50% by mass or less and a flux filled inside the steel sheath, the total mass of the flux-cored wire mass % relative to the total mass of the flux-cored wire, in a chemical composition containing 0.01 to 20.00% in total of rare earth oxides and excluding fluorides, nitrides, oxides, and metal carbonates %, a flux-cored wire for gas-shielded arc welding having a Cr content of 0 to less than 22.00%.
<2> The flux-cored wire according to <1>, which contains fluoride and has an F content of 0.003 to 30.000% in mass % with respect to the total mass of the flux-cored wire.
<3> The flux-cored wire according to <1> or <2>, which contains a nitride and has an N content of 0.003 to 15.00% in mass % with respect to the total mass of the flux-cored wire.
<4> The chemical composition, excluding fluorides, nitrides, oxides, and metal carbonates, is mass% with respect to the total mass of the flux-cored wire,
C: 0.003 to 0.500%,
Si: 0 to 3.50%,
Mn: 0 to 10.00%,
P: 0 to 0.030%,
S: 0 to 0.030%,
Cu: 0 to 10.00%,
Ni: 0 to 50.00%,
Cr: 0-10.00%
Mo: 0 to 50.00%,
Nb: 0 to 0.500%,
V: 0 to 0.500%,
W: 0 to 10.00%,
Sn: 0 to 10.00%,
Sb: 0 to 10.00%,
Ti: 0 to 0.500%,
Al: 0 to 1.000%,
B: 0 to 1.000%,
Mg: 0-2.000%,
Ca: 0 to 2.000%,
REM: 0 to 0.5000%,
The flux-cored wire according to any one of <1> to <3>, comprising Bi: 0 to 0.300% and the balance: Fe and impurities.
<5> from the group consisting of Ti oxide, Fe oxide, Ba oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, K oxide and Ca oxide including one or more selected specific oxides, in mass % with respect to the total mass of the flux-cored wire, and each of the specific oxides TiO ₂ , FeO, BaO, Na ₂ O, SiO ₂ , Any one of <1> to <4>, wherein the total content of the specific oxides is 10.00% or less in terms of ZrO ₂ , MgO, Al ₂ O ₃ , MnO ₂ , K ₂ O or CaO Flux-cored wire as described in Section 1.
<6> One or more specific metal carbonates selected from the group consisting of MgCO ₃ , Na ₂ CO ₃ , LiCO ₃ , CaCO ₃ , K ₂ CO ₃ , BaCO ₃ , FeCO ₃ , MnCO ₃ and SrCO ₃ The flux-cored wire according to any one of <1> to <5>, which contains a salt and has a total content of the specific metal carbonate of 10.00% or less in mass% with respect to the total mass of the flux-cored wire. wire.
<7> The flux-cored wire according to any one of <1> to <6>, the surface of which is coated with one or both of polytetrafluoroethylene oil and perfluoropolyether oil.
<8> The flux-cored wire according to any one of <1> to <7>, wherein the total mass % of the rare earth oxide with respect to the total mass of the flux-cored wire exceeds 0.20%.
<9> The flux according to any one of <1> to <8>, wherein the Cr content is 0 to less than 10.00% in the chemical composition excluding fluorides, nitrides, oxides, and metal carbonates. input wire.
<10> A method for producing a welded joint, comprising gas-shielded arc welding a steel material using the flux-cored wire according to any one of <1> to <9>.
<11> The method for producing a welded joint according to <10>, wherein in the gas-shielded arc welding step, welding is performed using a torch that does not have a suction nozzle.

Advantageous Effects of Invention According to the present disclosure, there is provided a flux-cored wire and a method for manufacturing a welded joint, in which welding workability is high and hot cracking of weld metal is suppressed in gas-shielded arc welding.

An embodiment that is an example of the present disclosure will be described.
In this specification, the numerical range represented by using "to" is, if the numerical value described before and after "to" is not attached with "more than" and "less than", these numerical values as lower and upper limits. In addition, a numerical range when "more than" or "less than" is attached to the numerical value described before and after "-" means a range that does not include these numerical values as the lower or upper limit.
In the numerical ranges described step by step in this specification, the upper limit of one step of the numerical range may be replaced with the upper limit of the other step of the numerical range. You may substitute the indicated values. Furthermore, the lower limit of a given stepwise numerical range may be replaced with the lower limit of another stepwise stated numerical range, or may be replaced with the values shown in the examples.
Moreover, "%" means "mass %" about content.
"0-" as the content (%) means that the component is optional and may not be contained.

<Flux-cored wire>
A flux-cored wire according to the present disclosure includes a steel sheath having a Ni content of 50% by mass or less and a flux filled inside the steel sheath.
A flux-cored wire according to the present disclosure is a flux-cored wire for gas-shielded arc welding, and contains a total of 0.01 to 20.00% rare earth oxide in mass% with respect to the total mass of the flux-cored wire, In addition, in the chemical composition excluding fluorides, nitrides, oxides and metal carbonates, the Cr content is 0 to less than 22.00% by mass with respect to the total mass of the flux-cored wire.
Hereinafter, reasons for limiting the requirements (including optional requirements) constituting the flux-cored wire according to the present disclosure will be specifically described.

The flux-cored wire according to the present disclosure contains 0.01-20.00% total rare earth oxides.
In the following description, "%" means "% by mass with respect to the total mass of the flux-cored wire" unless otherwise specified.

(rare earth oxide)
The flux-cored wire according to the present disclosure contains 0.01 to 20.00% in total of rare earth oxides (hereinafter also referred to as "REM oxides"), thereby improving welding workability in gas shielded arc welding. do. Although the reason for this is not clear, the inclusion of rare earth oxides in the flux-cored wire increases the solidification temperature of the slag, which suppresses dripping of the molten pool and improves welding workability (especially vertical welding). This is thought to improve
If REM is simply contained in the flux-cored wire as an alloy rather than as an oxide, REM tends to oxidize, and the amount of REM in the alloy becomes unstable, making it difficult to control the composition. It is assumed that On the other hand, the present inventors found that by adding REM, which is an oxide-generating element, as a REM oxide, the amount of REM in the oxide becomes constant and the amount of REM in the wire can be easily controlled. Furthermore, it was found that an increase in spatter can be suppressed and a decrease in mechanical properties can be suppressed.

In gas-shielded arc welding, from the viewpoint of improving welding workability, the lower limit of the content of rare earth oxides is preferably 0.05% or more, 0.10% or more, 0.15% or more, and 0.20%. exceed. Moreover, the upper limit of the content of the rare earth oxide is set to 20.00% or less because the effect of adding the rare earth oxide is saturated. If necessary, the upper limit of the content of rare earth oxides may be 15.00% or less, 10.00% or less, 5.00% or less, 1.00% or less, or 0.50% or less.

Here, the rare earth oxide means an oxide of a rare earth element. That is, the flux-cored wire according to the present disclosure includes Sc oxide, Y oxide, La oxide, Ce oxide, Pr oxide, Nd oxide, Pm oxide, Sm oxide, Eu oxide, Gd oxide , Tb oxide, Dy oxide, Ho oxide, Er oxide, Tm oxide, Yb oxide, and Lu oxide.
Among these, the rare earth oxide contained in the flux-cored wire according to the present disclosure is one selected from the group consisting of Y oxide, La oxide, and Ce oxide from the viewpoint of improving welding workability, or Two or more are preferred.

(Cr content: 0 to less than 22.00%)
Since Cr is not an essential component, the lower limit of Cr content in the chemical composition of the flux-cored wire, excluding fluorides, nitrides, oxides and metal carbonates, is 0%.
On the other hand, when the Cr content is 22.00% or more, spattering tends to increase and the workability tends to deteriorate, so the Cr content is made less than 22.00%. Details of the Cr content will be described later.
Here, the "oxides" excluded from the above chemical composition include the rare earth oxides (REM oxides).

(F content: 0.003 to 30.000%)
Flux-cored wires according to the present disclosure need not contain fluoride. Therefore, in the flux-cored wire according to the present disclosure, the lower limit of fluoride content is 0%.
On the other hand, fluoride has the function of reducing the amount of diffusible hydrogen in the weld metal and significantly improving the cold cracking resistance of the weld metal. This is because when welding is performed with a flux-cored wire, fluorine (F ⁻ ) in the flux combines with hydrogen (H ⁺ ) to form hydrogen fluoride (HF), and this HF is released out of the weld metal. It is speculated that In order to obtain this effect, the total F content is preferably 0.003% or more.
On the other hand, fluoride causes generation of fumes during welding. Therefore, when the flux-cored wire according to the present disclosure contains fluoride, it is preferable to further contain nitride so that the N content falls within the range described below. It has been found that the inclusion of nitride in the flux-cored wire according to the present disclosure suppresses fume generation during welding even when the wire contains fluoride. The reason for this is not clear, but since nitrogen has a boiling point lower than that of hydrogen fluoride (HF) (N ₂ ; −196° C., hydrogen fluoride (HF); +20° C.), the nitride is decomposed by the arc. Nitrogen (N) is generated and combined as nitrogen molecules (N ₂ ) to lower the arc temperature, thereby reducing the amount of high-temperature steam in the arc and thereby suppressing the generation of fumes. be.

When the flux-cored wire according to the present disclosure contains fluoride, the type of fluoride is not limited, but preferably _CaF2 , _MgF2 , LiF, _NaF , _K2ZrF6 , _K2SiF6 , and _K2SiF6 in the flux. It is preferable to contain one or more fluorides selected from the group consisting of Na ₃ AlF ₆ . According to these fluorides, all of Ca, Mg, Li, Na, K, Zr, Si, and Al produced by ionization combine with oxygen to reduce the amount of oxygen in the weld metal. Acts as a deoxidizing element. This is advantageous in improving the toughness and elongation of the weld metal.
When the flux-cored wire according to the present disclosure contains 0.003% or more of fluoride, the total mass proportion of fluoride contained in the flux-cored wire (preferably flux) according to the present disclosure is 0.003% in terms of F content. As long as it is above, the lower limit of the content of each fluoride is not particularly limited. In addition, since the F content indicates the amount of fluorine (F) contained in the fluoride in mass % with respect to the total mass of the flux-cored wire, the type of fluoride is the above-described preferred example of the fluoride. In this case, the F content is obtained from the following formula B.
Formula B: 0.487* _CaF2 +0.610* _MgF2 +0.732*LiF+0.452*NaF+0.402* _{K2ZrF6 +} 0.517* _{K2SiF6 + 0.543} * _Na3AlF6
Here, the chemical formulas of the fluorides in the formula B indicate mass % of the fluorides corresponding to the respective chemical formulas with respect to the total mass of the flux-cored wire. The coefficient of the chemical formula of each fluoride is calculated from the chemical formula weight of each fluoride.
When fluorides other than the preferred examples described above are included, the F content is calculated from the chemical formula weight of each fluoride according to the above formula B.
The lower limit of the F content is preferably 0.003% by mass relative to the total mass of the flux-cored wire, and is 0.005%, 0.010%, 0.015%, 0.020%, 0.020%, and 0.005%. 025% or 0.030%.
Preferred upper limits of the F content are 30.000%, 20.000%, 10.000%, and 3.000% by mass relative to the total mass of the flux-cored wire from the viewpoint of suppressing fume generation during welding. , 2.000%, 1.000%, 0.500%, 0.100%, or 0.050%.
Note that the F content in the flux-cored wire according to the present disclosure is measured by fluorescent X-ray analysis.

(N content: 0.003 to 15.00%)
Flux-cored wires according to the present disclosure need not contain nitrides. Therefore, in the flux-cored wire according to the present disclosure, the lower limit of nitride content is 0%.
On the other hand, nitrides have the function of reducing the amount of diffusible hydrogen in the weld metal and significantly improving the cold cracking resistance of the weld metal. Although the reason for this is not clear, one of the reasons is that N in the nitride combines with hydrogen (H) during welding to form ammonia (NH ₃ ), and this NH ₃ is released outside the weld metal. It is assumed that there is. The flux-cored wire according to the present disclosure may contain a nitride in the steel outer sheath, but at least the flux contains the nitride from the viewpoint of easily controlling the N content in the range described later with respect to the total mass of the wire. is preferred.

Nitrides that can be included in flux-cored wires according to the present disclosure include, for example, AlN, BN, _Ca3N2 , CeN, CrN, _{Cu3N ,} Fe4N _{, Fe3N} , _Fe2N , Mg 3N, _Mo2N , _{NbN , Si3N4} , TiN, VN, ZrN, _Mn2N , and _Mn4N . When the flux-cored wire according to the present disclosure contains one or more of these nitrides and does not contain nitrides other than these, the N content is represented by the following formula A .
Formula A: N content = 0.342 x AlN + 0.564 x BN + 0.189 x _{Ca3N2 +} 0.091 x CeN + 0.212 x CrN + 0.068 x _Cu3N + 0.059 x _Fe4N + 0.077 x _Fe3N + 0 .111 x Fe2N ₊ 0.161 x Mg3N + 0.068 x Mo2N _{+ 0.131} x NbN + _0.399 x _Si3N4 + 0.226 x TiN + 0.216 x VN + 0.133 x ZrN + 0.113 x Mn2N ₊ 0.06 × _Mn4N
Here, the chemical formulas of nitrides in formula A indicate the mass % of the nitrides corresponding to each chemical formula with respect to the total mass of the flux-cored wire. The coefficient of the chemical formula of each nitride is calculated from the chemical formula weight of each nitride.
When nitrides other than the nitrides listed above are included, the N content is calculated from the chemical formula weight of each nitride according to formula A above.

The flux-cored wire according to the present disclosure preferably contains 0.003% or more N with respect to the total mass of the flux-cored wire.

The amount of nitrogen contained in the flux-cored wire is analyzed and measured using JIS G1228:1997.
If the total N content in the entire flux-cored wire is 0.003% or more, the amount of diffusible hydrogen in the weld metal is sufficiently reduced, and the cold cracking resistance of the weld metal is improved.
In order to further reduce the amount of diffusible hydrogen in the weld metal, the lower limit of the N content is set to 0.005%, 0.008%, 0.010%, 0.015%, 0.020% or 0.022%. good too.
In the flux-cored wire of the present disclosure, the upper limit of the N content is not particularly limited from the viewpoint of reducing the amount of diffusible hydrogen, but considering that the steel outer skin is filled with flux, the N content The upper limit is 15.00%. The upper limit of N content may be 10.00%, 8.00%, or 5.00%.
Note that the ratio of N contained in the steel sheath to the entire wire is small, and the N content in the flux-cored wire according to the present disclosure can be adjusted mainly by the type and content of nitride contained in the flux. .

In addition, in the flux-cored wire according to the present disclosure, the N content of nitrogen contained as nitride in the flux is preferably 0.002% or more with respect to the total mass of the flux-cored wire. In order to further reduce the amount of diffusible hydrogen in the weld metal, the lower limits of the N content of nitrogen contained as nitrides in the flux are set to 0.005% and 0.008% with respect to the total mass of the flux-cored wire. %, 0.010%, 0.015%, 0.020% or 0.022%. Also, considering that the flux is filled inside the steel sheath, the upper limit of the N content of nitrogen contained in the flux as a nitride is 15% with respect to the total mass of the flux-cored wire. .00% is preferred and may be 10.00%, 8.00% or 5.00%.

The chemical composition, excluding fluorides, nitrides, oxides, and metal carbonates, of the flux-cored wire according to the present disclosure will now be described.
Each chemical component constituting the chemical composition described below may be contained in the steel sheath or may be contained in the flux. Moreover, when the flux-cored wire according to the present disclosure has a plating layer on the outer surface of the steel sheath, it may be included in the plating layer. In the following description, "chemical composition excluding fluorides, nitrides, oxides, and metal carbonates" may be simply referred to as "chemical composition."
The chemical composition, excluding fluorides, nitrides, oxides, and metal carbonates, of the flux-cored wire of the present disclosure is
C: 0.003 to 0.500%,
Si: 0 to 3.50%,
Mn: 0 to 10.00%,
P: 0 to 0.030%,
S: 0 to 0.030%,
Cu: 0 to 10.00%,
Ni: 0 to 50.00%,
Cr: 0-10.00%
Mo: 0 to 50.00%,
Nb: 0 to 0.500%,
V: 0 to 0.500%,
W: 0 to 10.00%,
Sn: 0 to 10.00%,
Sb: 0 to 10.00%,
Ti: 0 to 0.500%,
Al: 0 to 1.000%,
B: 0 to 1.000%,
Mg: 0-2.000%,
Ca: 0 to 2.000%,
REM: 0 to 0.5000%,
It is preferable that Bi: 0 to 0.300% and balance: Fe and impurities.

(C: 0.003-0.500%)
C is an important element for ensuring the yield strength and tensile strength of the weld metal through solid-solution strengthening. When the C content in the chemical composition of the flux-cored wire is 0.003% or more, the yield strength and tensile strength of the weld metal can be sufficiently secured.
On the other hand, since the C content in the chemical composition of the flux-cored wire is 0.500% or less, the C content in the weld metal is kept at an appropriate amount, and excessive increases in the yield strength and tensile strength of the weld metal are suppressed. It is possible to suppress the deterioration of the toughness of the weld metal.
Therefore, in order to stably ensure all of the toughness, yield strength, and tensile strength of the weld metal, the lower limit of the C content in the chemical composition of the flux-cored wire is preferably 0.003%. It is preferable to set the upper limit of the C content in the chemical composition of the cored wire to 0.500%. If necessary, the lower limit of the C content may be 0.010%, 0.020%, 0.030%, 0.040%, 0.050%, or 0.060%. Similarly, the upper limit of the C content may be 0.450%, 0.400%, 0.350%, 0.300%, or 0.250%.

(Si: 0 to 3.50%)
Since Si is not an essential component, the lower limit of the Si content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Si is a deoxidizing element and has the function of reducing the amount of oxygen in the weld metal and increasing the cleanliness of the weld metal. However, if the Si content is 3.50% or less, it is possible to suppress deterioration in the toughness of the weld metal, so this is preferably set as the upper limit. In order to stably secure the toughness of the weld metal, the upper limit of Si may be 3.00%, 2.00% or 1.00%. In order to obtain the above effects, the lower limit of the Si content may be 0.40%, 0.45%, 0.50%, or 0.60%.

(Mn: 0 to 10.00%)
Since Mn is not an essential component, the lower limit of Mn content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Mn is an effective element for securing the hardenability of the weld metal and increasing the strength of the weld metal. When the Mn content in the chemical composition of the flux-cored wire is 10.00% or less, the intergranular embrittlement susceptibility of the weld metal is reduced, and a decrease in the toughness of the weld metal can be suppressed. Therefore, it is preferable to set the upper limit of the Mn content to 10.00%. Preferably, the upper limit of Mn content is 9.50%, 9.00%, 8.00%, or 6.00%. In order to obtain the above effects, the lower limit of the Mn content may be 0.40%, 0.45%, 0.50%, or 0.60%.

(P: 0-0.030%)
P is an impurity element, and from the viewpoint of suppressing deterioration of the toughness of the weld metal, it is preferable to reduce the P content in the flux-cored wire as much as possible. Therefore, the lower limit of the P content in the chemical composition of the flux-cored wire is 0%. Moreover, if the P content in the chemical composition of the flux-cored wire is 0.030% or less, it is possible to suppress the deterioration of the toughness of the weld metal. In order to effectively suppress solidification cracking of the weld metal, the P content in the chemical composition of the flux-cored wire is more preferably 0.020% or less, 0.015% or less, or 0.010% or less. be.
However, since an extreme reduction in the P content results in an increase in manufacturing cost, the P content is preferably 0.003% or more from the viewpoint of reducing the cost of removing P.

(S: 0-0.030%)
S is also an impurity element, and from the viewpoint of suppressing deterioration of the toughness and ductility of the weld metal, it is preferable to reduce the S content in the flux-cored wire as much as possible. Therefore, the lower limit of the S content in the chemical composition of the flux-cored wire is 0%. Moreover, if the S content in the chemical composition of the flux-cored wire is 0.030% or less, it is possible to suppress deterioration in the toughness and ductility of the weld metal. The S content in the chemical composition of the flux-cored wire is more preferably 0.020% or less, 0.010% or less, 0.008% or less, 0.006% or less, or 0.005% or less.
However, since an extreme reduction in the S content results in an increase in manufacturing costs, the S content is preferably 0.003% or more from the viewpoint of reducing the S-free cost.

(Cu: 0 to 10.00%)
Since Cu is not an essential component, the lower limit of Cu content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Cu has the effect of improving the strength and toughness of the weld metal. In order to sufficiently obtain the effect, the Cu content in the chemical composition of the flux-cored wire is preferably 0.01% or more. Cu may be included in the plating on the surface of the steel jacket of the flux-cored wire, and may be included in the flux either singly or as an alloy. Cu plating also has the effect of improving rust resistance, electrical conductivity, and tip wear resistance.
Therefore, the Cu content in the chemical composition of the flux-cored wire is the total amount of Cu contained in the steel sheath and flux, and Cu contained in the plating on the wire surface.
On the other hand, when the Cu content in the chemical composition of the flux-cored wire is 10.00% or less, it is possible to suppress the deterioration of the toughness of the weld metal. Therefore, it is preferable to set the Cu content to 10.00% or less. The upper limit of the Cu content in the chemical composition of the flux-cored wire is preferably 9.00%, 8.00%, 7.00%, 6.00%, 5.00%, 4.00%, 3.00 %, or 2.00%.

(Ni: 0 to 50.00%)
Since Ni is not an essential component, the lower limit of the Ni content in the chemical composition of the flux-cored wire is 0%.
Ni improves the toughness of the weld metal by solid solution toughening of Ni. In order to obtain this effect, the Ni content is preferably 0.30% or more, 0.50% or more, or 1.00% or more. On the other hand, when the Ni content is 50.00% or less, it is possible to suppress deterioration of the hot cracking resistance of the weld metal. Therefore, the upper limit of the Ni content in the chemical composition of the flux-cored wire is preferably 50.00% or less. The upper limit of the Ni content may be 45.00%, 40.00%, or 35.00%.

(Cr: 0 to 10.00%)
Since Cr is not an essential component, the lower limit of the Cr content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Cr is an effective element for securing the hardenability of the weld metal and increasing the strength of the weld metal. As described above, Cr may be included at less than 22.00%. However, by setting the Cr content in the chemical composition of the flux-cored wire to 10.00% or less, it is possible to suppress the decrease in the toughness of the weld metal. Therefore, the upper limit of the Cr content in the chemical composition of the flux-cored wire is preferably 10.00% or less, more preferably less than 10.00%. More preferably, the upper limit of Cr content is 9.50%, 9.00%, 8.00%, or 6.00%. If necessary, the lower limit of Cr content may be 0.01%, 0.05%, 0.10%, or 0.20%.

(Mo: 0-50.00%)
Since Mo is not an essential component, the lower limit of the Mo content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Mo has the effect of improving the hardenability of the weld metal, so it is an effective element for increasing the strength of the weld metal. In order to obtain this effect, it is preferable to set the lower limit of the Mo content in the chemical composition of the flux-cored wire to 0.01%, 0.05%, 0.10% or 0.15%. On the other hand, by setting the Mo content in the chemical composition of the flux-cored wire to 50.00% or less, it is possible to suppress deterioration in the toughness of the weld metal. Therefore, the Mo content in the chemical composition of the flux-cored wire is preferably 50.00% or less. The upper limit of the Mo content in the chemical composition of the flux-cored wire is preferably 48.00%, 45.00%, 40.00%, 30.00% or 10.00%.

(Nb: 0 to 0.500%)
Since Nb is not an essential component, the lower limit of the Nb content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Nb forms fine carbides in the weld metal, and these fine carbides cause precipitation strengthening in the weld metal, so Nb improves the tensile strength of the weld metal. In order to sufficiently obtain the effect, it is preferable to set the lower limit of the Nb content in the chemical composition of the flux-cored wire to 0.005%, 0.010%, 0.015% or 0.020%.
On the other hand, when the Nb content in the chemical composition of the flux-cored wire is 0.500% or less, the formation of coarse precipitates due to Nb in the weld metal is suppressed, and a decrease in the toughness of the weld metal can be suppressed. Therefore, the upper limit of the Nb content in the chemical composition of the flux-cored wire is preferably 0.500%, more preferably 0.450%, 0.400%, 0.300%, or 0.200%. be.

(V: 0-0.500%)
Since V is not an essential component, the lower limit of the V content in the chemical composition of the flux-cored wire is 0%.
On the other hand, since V improves the hardenability of the weld metal, it is an effective element for increasing the strength of the weld metal. In order to sufficiently obtain the effect, it is preferable to set the lower limit of the V content in the chemical composition of the flux-cored wire to 0.001%, 0.010%, 0.030% or 0.050%.
On the other hand, when the V content in the chemical composition of the flux-cored wire is 0.500% or less, the amount of precipitation of V carbide in the weld metal does not increase excessively, and excessive hardening of the weld metal is suppressed. It is possible to suppress the decrease in toughness of Therefore, the upper limit of the V content in the chemical composition of the flux-cored wire is preferably 0.500%, more preferably 0.400%, 0.300%, 0.200%, 0.100%, or 0.080%.

(W: 0-10.00%)
W is an effective element for improving the corrosion resistance of the weld metal, but W is not an essential component. Therefore, the lower limit of the W content in the chemical composition of the flux-cored wire is 0%. On the other hand, when the W content in the chemical composition of the flux-cored wire is 10.00% or less, cracking of the weld metal can be suppressed. Therefore, it is preferable to set the upper limit of the W content in the chemical composition of the flux-cored wire to 10.00%. More preferably, the upper limit of W content is 9.50%, 9.00%, 8.00%, or 6.00%. If necessary, the lower limit of W content may be 0.01%, 0.03%, 0.50%, or 0.60%.

(Sn: 0 to 10.00%)
Sn is an effective element for improving the corrosion resistance of the weld metal, but Sn is not an essential component. Therefore, the lower limit of the Sn content in the chemical composition of the flux-cored wire is 0%. On the other hand, when the Sn content in the chemical composition of the flux-cored wire is 10.00% or less, cracking of the weld metal can be suppressed. Therefore, it is preferable to set the upper limit of the Sn content in the chemical composition of the flux-cored wire to 10.00%. More preferably, the upper limit of Sn content is 9.50%, 9.00%, 8.00%, or 6.00%. The lower limit of the Sn content may be 0.01%, 0.03%, 0.50%, or 0.60% as required.

(Sb: 0 to 10.00%)
Sb is an effective element for improving the corrosion resistance of weld metal, but Sb is not an essential component. Therefore, the lower limit of the Sb content in the chemical composition of the flux-cored wire is 0%. On the other hand, when the Sb content in the chemical composition of the flux-cored wire is 10.00% or less, cracking of the weld metal can be suppressed. Therefore, it is preferable to set the upper limit of the Sb content in the chemical composition of the flux-cored wire to 10.00%. More preferably, the upper limit of Sb content is 9.50%, 9.00%, 8.00%, or 6.00%. If necessary, the lower limit of the Sb content may be 0.01%, 0.03%, 0.50%, or 0.60%.

(Ti: 0 to 0.500%)
Since Ti is not an essential component, the lower limit of the Ti content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Ti is a deoxidizing element and has the effect of reducing the amount of oxygen in the weld metal. In addition, a small amount of Ti contained in the chemical composition of the flux-cored wire remains in the weld metal and fixes solid solution N, so it has the effect of alleviating the adverse effect of solid solution N on the toughness of the weld metal. Therefore, the chemical composition of the flux-cored wire may contain 0.001% or more, 0.010% or more, 0.030% or more, or 0.050% or more of Ti.
On the other hand, when the Ti content in the chemical composition of the flux-cored wire is 0.500% or less, the generation of excessive precipitates in the weld metal is suppressed, and the deterioration of toughness can be suppressed. When Ti is included in the chemical composition of the flux-cored wire, generally ferrotitanium (an alloy of iron and titanium) is included in the flux. The upper limit of the Ti content in the chemical composition of the flux-cored wire is preferably 0.500%, more preferably 0.400%, 0.300%, 0.200%, 0.100%, or 0.400%. 080%.
In addition, when the flux-cored wire according to the present disclosure contains Ti oxide, the above Ti content is the content other than Ti constituting the Ti oxide.

(Al: 0 to 1.000%)
Since Al is not an essential component, the lower limit of the Al content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Al is a deoxidizing element, and like Si, it reduces the amount of oxygen in the weld metal and has the effect of improving the cleanliness of the weld metal. However, if the Al content is 1.000% or less, it is possible to suppress the deterioration of the toughness of the weld metal. Therefore, the Al content in the chemical composition of the flux-cored wire is preferably 1.000% or less. In order to stably secure the toughness of the weld metal, the upper limit of the Al content may be 0.950%, 0.900%, 0.850% or 0.800%. If necessary, the lower limit of Al content may be 0.005%, 0.010%, 0.050%, 0.100%, 0.150% or 0.200%.

(B: 0 to 1.000%)
Since B is not an essential component, the lower limit of the B content in the chemical composition of the flux-cored wire is 0%.
On the other hand, B combines with solute N in the weld metal to form BN, so it has the effect of reducing the adverse effect of solute N on the toughness of the weld metal. Further, since B increases the hardenability of the weld metal, it also has the effect of improving the strength of the weld metal. Therefore, the chemical composition of the flux-cored wire may contain 0.0005% or more of B.
On the other hand, when the B content in the chemical composition of the flux-cored wire is 1.000% or less, the amount of B in the weld metal does not increase excessively, and coarse BN and B compounds such as Fe ₂₃ (C, B) ₆ are not generated. Formation is suppressed, and a decrease in the toughness of the weld metal can be suppressed. Therefore, the upper limit of the B content in the chemical composition of the flux-cored wire is preferably 1.000%, more preferably 0.900%, 0.800% or 0.700%.

(Mg: 0 to 2.000%)
Since Mg is not an essential component, the lower limit of the Mg content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Mg is a deoxidizing element, and like Al, it reduces the amount of oxygen in the weld metal and has the effect of improving the cleanliness of the weld metal. However, by setting the Mg content in the chemical composition of the flux-cored wire to 2.000% or less, it is possible to suppress the amount of spatters and fumes generated by the violent reaction between Mg and oxygen in the arc. Therefore, it is preferable to set the Mg content in the chemical composition of the flux-cored wire to 2.000% or less. A preferred lower limit of the Mg content in the chemical composition of the flux-cored wire is 0.150%, 0.200%, 0.250%, or 0.300%. Preferred upper limits for the Mg content in the chemical composition of the flux-cored wire are 1.700%, 1.600%, 1.500%, 1.400%, 1.000% or 0.900%.

(Ca: 0 to 2.000%)
(REM: 0-0.5000%)
Since Ca and REM are not essential components, the lower limits of Ca content and REM content in the chemical composition of the flux-cored wire are both 0%.
On the other hand, both Ca and REM change the structure of sulfides in the weld metal and refine the size of the sulfides and oxides, thereby improving the ductility and toughness of the weld metal. . Therefore, the Ca content in the chemical composition of the flux-cored wire may be 0.002% or more, and the REM content in the chemical composition of the flux-cored wire may be 0.0002% or more.
On the other hand, by reducing the Ca content and REM content in the chemical composition of the flux-cored wire, the amount of spatter can be suppressed and the weldability can be improved. Therefore, the upper limit of the Ca content in the chemical composition of the flux-cored wire is preferably 2.000%, and the upper limit of the REM content in the chemical composition of the flux-cored wire is preferably 0.5000%.
In the present disclosure, "REM" included in the chemical composition excluding fluorides, nitrides, oxides, and metal carbonates is an alloy, which is not included as at least the above-described "rare earth oxide" indicates
Here, REM is a generic term for a total of 17 elements including Sc, Y and lanthanoids, and the REM content refers to the total REM content. Also, REM is generally contained in the misch metal. For this reason, for example, a misch metal may be added to the alloy so that the content of REM is within the above range.

(Bi: 0 to 0.300%)
Since Bi is not an essential component, the lower limit of the Bi content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Bi is an element that improves the releasability of slag. In order to sufficiently obtain the effect, the Bi content in the chemical composition of the flux-cored wire is preferably 0.005% or more, 0.010% or more, or 0.012% or more.
On the other hand, when the Bi content in the chemical composition of the flux-cored wire is 0.300% or less, the occurrence of solidification cracking in the weld metal can be suppressed. Therefore, the upper limit of the Bi content in the chemical composition of the flux-cored wire is preferably 0.300%. The upper limit of the Bi content in the chemical composition of the flux-cored wire may preferably be 0.250%, 0.200% or 0.100%.

(Remainder: Fe and impurities)
The other balance constituents in the flux-cored wire according to the present disclosure are Fe and impurities. The remaining Fe is, for example, Fe contained in the steel outer sheath, Fe contained in the alloy powder contained in the flux, and the like.
In addition, impurities are components derived from raw materials or mixed due to various factors in the manufacturing process when the flux-cored wire is industrially manufactured, and have an adverse effect on the flux-cored wire according to the present disclosure. It means what is permissible within the scope of

(Total content of specific oxides: 0 to 10.00%)
The flux-cored wire according to the present disclosure includes Ti oxide, Fe oxide, Ba oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, K oxide and Ca One or two or more specific oxides selected from the group consisting of oxides may be included, and the total content of the specific oxides is preferably 10.00% or less. In the present disclosure, the group consisting of Ti oxide, Fe oxide, Ba oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, K oxide and Ca oxide Oxide contained in may be simply abbreviated as "specific oxide". Also, the total content of each of the specific oxides may be abbreviated as "the total content of the specific oxides". The specific oxides do not include the aforementioned "rare earth oxides".
The total content of specific oxides is obtained by converting each of the specific oxides to TiO ₂ , FeO, BaO, Na ₂ O, SiO ₂ , ZrO ₂ , MgO, Al ₂ O ₃ , MnO ₂ , K ₂ O or CaO. and obtain the sum of them. That is, the total content of the specific oxides is the _TiO2 conversion value of the total Ti oxide content, the FeO conversion value of the total Fe oxide content, the BaO conversion value of the total Ba oxide content, and the total Na Oxide content converted to _Na2O , total Si oxide content converted to _SiO2 , total Zr oxide content converted to ZrO2, _total Mg oxide content converted to MgO, Al ₂ O ₃ conversion value of total Al oxide content, MnO ₂ conversion value of total Mn oxide content, K ₂ O conversion value of total K oxide content, and total Ca oxide content represents the total CaO conversion value of
For example, the flux-cored wire according to the present disclosure contains TiO ₂ , FeO, BaO, Na ₂ O, SiO ₂ , ZrO ₂ , MgO, Al ₂ O ₃ , MnO ₂ , K ₂ O and CaO as the specific oxides. When only one or more oxides are included, the total content of the specific oxides is TiO ₂ , FeO, BaO, Na ₂ O, SiO ₂ , ZrO ₂ , MgO, Al ₂ O ₃ , MnO ₂ , Obtained as the total value of each content of K ₂ O and CaO.
Since the flux-cored wire according to the present disclosure does not include the specific oxide as an essential component, the lower limit of the total amount of the specific oxide in the flux-cored wire is 0%.
On the other hand, the specific oxide has the effect of maintaining a good weld bead shape and the effect of improving vertical weldability. In addition, Na oxide, K oxide, Mg oxide, Fe oxide, etc. also have the effect of stabilizing the arc. In order to obtain such effects, the total content of the specific oxides is preferably 0.05% or more. In order to exhibit these effects more effectively, the lower limit of the total content of the specific oxides may be 0.10%, 0.15%, or 0.20%. On the other hand, when the total content of the specific oxides is 10.00% or less, it is possible to suppress the occurrence of slag entrainment. Therefore, the upper limit of the total content of the specific oxides is preferably 10.00%, 9.00%, 8.00%, 7.00%, 6.00%, 3.00%, 2 0.00%, 1.00% or 0.50%.

The content of the specific oxide in the flux-cored wire according to the present disclosure does not need to be limited for each type of specific oxide, but from the viewpoint of suppressing toughness deterioration due to an excessive increase in the amount of oxygen in the weld metal, For example, a suitable composition is Si oxide: 0.08% or more and 0.95% or less, Zr oxide: 0.80% or less, and Al oxide: 0.50% or less.

Here, measurement of the content of each specific oxide and the total content of specific oxides in the flux-cored wire according to the present disclosure will be described.
First, regarding the content of Ti oxide, the mass of Ti present as a specific oxide contained in the flux-cored wire is analyzed using an X-ray fluorescence spectrometer. Specifically, the wire is polished to expose a longitudinal section (a section parallel to the longitudinal direction of the wire: L section) at a position ½ of the wire diameter φ, and the section is analyzed. For example, if TiO ₂ , Ti ₂ O ₃ , Ti ₃ O ₅ are detected by analysis, the mass % of each Ti oxide is [TiO ₂ ], [Ti ₂ O ₃ ], [Ti ₃ O ₅ ], and the sum of TiO ₂ equivalent values of Ti oxides is represented by [converted TiO ₂ ], it is calculated by the following formula C1.
[Converted TiO ₂ ]=(0.60×[TiO ₂ ]+0.67×[Ti ₂ O ₃ ]+0.64×[Ti ₃ O ₅ ])×1.67 Equation C1
The coefficients (0.60, 0.67, 0.64) in Equation C1 are coefficients for calculating the amount of Ti contained in each oxide, and the multiplier at the end (1.67) is the It is a multiplier for calculating the _TiO2 conversion value from the total amount of Ti present as a substance.

Here, how to obtain the coefficient will be described. Assuming that an oxide of M _x O _y (eg, TiO ₂ , Ti ₂ O ₃ , Ti ₃ O ₅ ) is detected, the coefficient for M _x O _y is calculated by Equation C2 below.
[Atomic weight of M element] x x/([Atomic weight of M element] x x + [Atomic weight of oxygen] x y) Formula C2
0.60, 0.67, and 0.64 in Equation C1 correspond to the coefficients obtained by Equation C2 above.
Also, how to obtain the multiplier for calculating the conversion value will be described. A multiplier for converting to M _a O _b (eg, TiO ₂ ) is calculated by the following formula C3.
([atomic weight of element M]×a+[atomic weight of oxygen]×b)/[atomic weight of element M×a] Formula C3
1.67 in the formula C1 corresponds to the multiplier obtained by the above formula C3.
The oxide may also be a compound in which two metal elements are combined. In that case, the coefficient is obtained by M _x O _y M ² _z (eg TiO ₃ ·Fe, that is, an oxide where M = Ti, M ² = Fe, x = 1, y = 3, z = 1) If it is detected, it is calculated by the following formula C4.
[Atomic weight of M element] x x/([Atomic weight of M element] x x + [Atomic weight of oxygen] x y + [Atomic weight of ^M2 element] x z) Formula C4
The content of specific oxides other than Ti oxides is also measured by using fluorescent X-ray analysis in the same manner as the content of Ti oxides described above.

(Total content of specific metal carbonates: 0 to 10.00%)
Flux-cored wires according to the present disclosure need not contain metal carbonates. Therefore, in the flux-cored wire according to the present disclosure, the lower limit of the metal carbonate content is 0%.
Metal carbonates, on the other hand, are ionized by the arc and generate _CO2 gas. _CO2 gas lowers the hydrogen partial pressure in the welding atmosphere and reduces the amount of diffusible hydrogen in the weld metal. To achieve this effect, flux-cored wires according to the present disclosure may include metal carbonates. In particular, it is preferable to include a metal carbonate in the flux of the flux-cored wire.
The type and composition of the metal carbonate included in the flux-cored wire according to the present disclosure are not limited. However, the type of metal carbonate contained in the flux-cored wire is the group consisting of _MgCO3 , _{Na2CO3 , LiCO3 , CaCO3 , K2CO3 ,} BaCO3, _FeCO3 , _MnCO3 , and SrCO3 ( Hereinafter, the metal carbonates included in this group may be abbreviated as "specific metal carbonates").
In order to obtain the above effect, it is preferable to contain the specific metal carbonate, that is, it is preferable that the total content of the specific metal carbonate exceeds 0%. In order to exhibit these effects more effectively, the lower limit of the total content of specific metal carbonates may be set to 0.05%.
On the other hand, when the content of the specific metal carbonate is 10.00% or less, it is possible to suppress the occurrence of sagging of the weld bead and improve welding workability. Therefore, when the flux-cored wire according to the present disclosure contains the specific metal carbonate, the upper limit of the total content of the specific metal carbonate is preferably 10.00%. If necessary, the upper limit of the content of the specific metal carbonate is changed to 9.00%, 8.00%, 7.00%, 6.00%, 3.00%, 2.00%, 1.00 % or 0.50%.
The content of each specific metal carbonate and the total content of the specific metal carbonate in the flux-cored wire according to the present disclosure are measured by using fluorescent X-ray analysis in the same manner as the content of Ti oxide described above. .

A flux-cored wire according to the present disclosure may further comprise a lubricant applied to the surface. The lubricant applied to the surface of the wire has the effect of improving the feedability of the wire during welding. Various types of lubricants (for example, vegetable oils such as palm oil) can be used as lubricants for welding wires. oils) and perfluoropolyether oils (PFPE oils) are preferably used. Also, as described above, the flux-cored wire according to the present disclosure may further comprise plating formed on the wire surface. In this case, the lubricant is applied to the surface of the plating.

Although the amount of hydrogen contained in the flux-cored wire according to the present disclosure is not particularly limited, it is preferably 12 ppm or less with respect to the total mass of the flux-cored wire in order to reduce the amount of diffusible hydrogen in the weld metal. The amount of hydrogen in the flux-cored wire can increase due to moisture intrusion into the flux-cored wire during storage of the flux-cored wire. Therefore, when the period from wire manufacture to wire use is long, it is desirable to prevent moisture intrusion by means described later.

(Steel skin)
The steel jacket of the flux-cored wire according to the present disclosure has a Ni content of 50% by mass or less. If the Ni content exceeds 50% by mass, hot cracking of the weld metal is likely to occur, so the Ni content in the steel outer skin is made 50% by mass or less. The Ni content in the steel outer skin is preferably 40% by mass or less, more preferably 20% by mass or less.
In addition, the steel sheath of the flux-cored wire according to the present disclosure is not particularly limited as long as the above-mentioned items are satisfied. : 0-0.1%, Si: 0-0.10%, Mn: 0-3.00%, P: 0-0.030%, S: 0-0.020%, Al: 0-0. 1%, and N: 0 to 0.030%, the balance being iron and impurities.

Normally, the steel skin also contains N as an impurity, but the N contained in the flux as a nitride reduces the amount of diffusible hydrogen in the weld metal than the N contained in the steel skin. Highly effective. The detailed mechanism is unknown, but since the steel skin is in contact with the shielding gas, the temperature is lower than that of the flux. It is presumed that this is because it is difficult to
From the above point of view, in the flux-cored wire according to the present disclosure, the N content of nitrogen contained as nitride in the flux is preferably 0.002% or more with respect to the total mass of the flux-cored wire. In addition, if the steel sheath contains a large amount of nitrogen, the drawability of the steel is inferior and the wire may break. Therefore, in general, the lower the N content (%) in the steel outer skin, the better.

(wire shape)
Next, the shape (wire structure) of the flux-cored wire according to the present disclosure will be described.
Normally, flux-cored wire is a wire (sometimes called a seamless wire) that has a slit-shaped gap (seamless shape) because the seam of the steel skin is welded to the seam of the steel skin. Therefore, it is distinguished from a wire having a shape including slit-like gaps.

Any shape can be employed in the flux-cored wire according to the present disclosure. However, in order to suppress the occurrence of cold cracks in the weld metal, it is preferable that the steel skin has no slit-like gaps. H (hydrogen) that enters the welded portion during welding diffuses into the weld metal and the material to be welded, accumulates in the stress concentration portion, and causes cold cracking. There are various sources of H, but when welding is performed with the cleanliness of the weld and the gas shielding conditions strictly controlled, the moisture (H ₂ O) contained in the wire is the main source of H. and the amount of this moisture strongly affects the amount of diffusible hydrogen in the welded joint.
When the steel skin has seams, moisture in the atmosphere easily enters the flux through the seams. For this reason, it is desirable to prevent moisture in the atmosphere from entering the flux through the steel skin after the wire is manufactured and before the wire is used by removing the seam of the steel skin. If the steel skin has seams and the time between wire manufacture and wire use is long, the entire flux-cored wire is vacuum-packaged to prevent ingress of sources of H, such as moisture, or It is desirable to store the flux-cored wire in a container that can be kept dry.

(wire diameter)
Although the diameter of the flux-cored wire according to the present disclosure is not particularly limited, it is, for example, φ1.0 to φ2.0 mm. Incidentally, the diameter of a general flux-cored wire is φ1.2 to φ1.6 mm.

(Filling rate)
The filling rate of the flux-cored wire according to the present disclosure is not particularly limited as long as the above conditions are satisfied. In view of typical flux-cored wire filling rates, the lower limit of the filling rate of flux-cored wires according to the present disclosure may be, for example, 8%, 10%, or 12%. Also, the upper limit of the filling rate of the flux-cored wire according to the present disclosure may be, for example, 28%, 25%, 22%, 20%, or 17%.

<Manufacturing method of flux-cored wire>
Next, a method for manufacturing a flux-cored wire according to the present disclosure will be described.
Note that the manufacturing method described below is an example, and the method of manufacturing the flux-cored wire according to the present disclosure is not limited to the following method.

(In the case of flux-cored wire with seamless shape)
A method for producing a flux-cored wire having a seamless shape includes a step of preparing a flux, a step of forming a steel strip using forming rolls while feeding it in the longitudinal direction to obtain a U-shaped open pipe, and a step of forming an open pipe. a step of supplying flux into the open pipe through the opening; a step of butt-welding opposite edge portions (both ends in the circumferential direction) of the opening of the open pipe to obtain a seamless pipe; Obtaining a flux-cored wire having a wire diameter; and annealing the flux-cored wire during or after the drawing process.
The amount of rare earth oxides in the flux-cored wire, and the amount of nitrides, fluorides, specific oxides, specific metal carbonates, and chemical composition of the flux-cored wire are within the above-described predetermined ranges. prepared as follows. The flux filling rate, which is determined by the width and thickness of the steel strip, which is the material of the steel outer sheath, and the flux filling amount, etc., also affects the amount of nitrides, fluorides, specific oxides, and specific metals in the flux-cored wire. It should be noted that it affects the amount of carbonate and the chemical composition.

Butt welding is performed by electric resistance welding, laser welding, TIG welding, or the like.
In addition, the flux-cored wire is annealed during the wire drawing process or after the wire drawing process is completed in order to remove moisture in the flux-cored wire. In order to reduce the H content of the flux-cored wire to 12 ppm or less, the annealing temperature is preferably 650° C. or higher and the annealing time is preferably 4 hours or longer. Note that the annealing temperature is preferably 900° C. or lower in order to prevent the flux from deteriorating.

A cross-section of a butt-seam-welded, slit-like, gapless flux-cored wire is polished and etched to show weld marks, but not to be etched. Therefore, it is sometimes called seamless as described above. For example, "Introduction to Welding and Joining Techniques" (2008) Sanpo Publishing, edited by The Welding Society, p. 111 describes a butt-seam welded, slit-free, flux-cored wire as a seamless type wire. A flux-cored wire without slit-like gaps can be obtained even if the gaps in the steel outer sheath of the flux-cored wire are brazed.

(For flux-cored wires with slit-like gaps)
A method for manufacturing a flux-cored wire having a slit-like gap is formed by forming an open tube and butting the ends of the open tube instead of butt-welding both ends of the open tube in the circumferential direction to obtain a seamless tube. The method is the same as the method for producing a flux-cored wire having a seamless shape, except that it includes a step of obtaining a slit-shaped gapped tube. The method of manufacturing a flux-cored wire having slit-like gaps may further comprise crimping the ends of the butted open tubes.
In a method for manufacturing a flux-cored wire having slit-like gaps, a pipe having slit-like gaps is drawn.

<Method for manufacturing welded joint>
Next, a method for manufacturing a welded joint (welding method) according to the present disclosure will be described.
A method of manufacturing a welded joint according to the present disclosure comprises gas-shielded arc welding a steel material using the flux-cored wire according to the present disclosure described above.

The gas-shielded arc welding process does not require the use of a special torch, such as a torch with a suction nozzle, and welding can be performed using a normal torch.

In the method for manufacturing a welded joint according to the present disclosure, gas-shielded arc welding is used as the welding method.
In the method for manufacturing a welded joint according to the present disclosure, the type of steel material (material to be welded) that is the base material of the welded joint is not particularly limited. For example, the tensile strength is 590 MPa or more and 1700 MPa or less, and it can be suitably used for a high-strength steel plate having a thickness of 20 mm or more.

A method for manufacturing a welded joint according to the present disclosure uses the welding wire according to the present disclosure, which has high welding workability and can suppress hot cracking of the weld metal. Therefore, even when steel materials with high hot cracking susceptibility are welded by the method for manufacturing a welded joint according to the present disclosure, the welding operation can be easily performed, and the occurrence of hot cracking in the weld metal can be suppressed. . In addition, the joint obtained by the method for manufacturing a welded joint according to the present disclosure may be an undermatched joint in which the tensile strength of the weld metal is lower than the tensile strength of the base metal of the steel plate.

In the method for manufacturing a welded joint according to the present disclosure, in one or more of the first pass to the final pass, the base steel plate is gas-shielded arc welded using the flux-cored wire for gas-shielded arc welding according to the present disclosure. Have a process. If the welding is only one pass, the flux cored wire for gas shielded arc welding according to the present disclosure is used in that one pass.
The type of base material steel plate (base material) is not particularly limited. The polarity of the flux-cored wire may be either positive or negative, but preferably positive, because the effect on the amount of diffusible hydrogen in the weld metal and the amount of spatter generated is negligible.

The type of shielding gas used in the method of manufacturing a welded joint according to the present disclosure is not particularly limited. The method for manufacturing a welded joint according to the present disclosure can exhibit excellent welding workability and obtain a welded joint having high strength, high toughness, and high fatigue strength regardless of the type of shielding gas. As the shielding gas in the method for manufacturing a welded joint according to the present disclosure, 100% by volume carbon dioxide gas, a mixed gas of Ar and 3 to 30% by volume _CO2 , etc., which are commonly used, can be preferably used. . Also, the shielding gas during welding using the flux-cored wire according to the present disclosure may contain 5% by volume or less of O ₂ gas. Since these gases are inexpensive, welding using these gases is advantageous for industrial use.
These gases normally produce a large amount of spatter and deteriorate welding workability when used in combination with a rutile flux-cored wire. However, since the method for manufacturing a welded joint according to the present disclosure uses the flux-cored wire according to the present disclosure, which can sufficiently suppress the amount of spatter, even when these gases are shield gases, good welding workability can be achieved. can be demonstrated.

The welding posture in the method for manufacturing a welded joint according to the present disclosure is not particularly limited. The method for manufacturing a welded joint according to the present disclosure can exhibit good welding workability regardless of whether the welding posture is a downward posture, a lateral posture, a vertical posture, or an upward posture.

A welded joint obtained by the method for manufacturing a welded joint according to the present disclosure includes a base material steel plate (base material) and a weld formed from a weld metal and a weld heat affected zone. The base material of the welded joint is not particularly limited. Since the welded joint according to the present disclosure is manufactured using the flux-cored wire according to the present disclosure in which the amount of rare earth oxides and the like is preferably controlled, hot cracking of the weld metal is suppressed.

By performing gas-shielded arc welding using the flux-cored wire according to the present disclosure, a welded portion having excellent hot crack resistance can be obtained.

Next, the feasibility and effect of the present disclosure will be described in more detail by way of examples and comparative examples. All are included in the technical scope of the present disclosure.

(manufacture of flux-cored wire)
The flux-cored wires of Examples and Comparative Examples were manufactured by the method described below.
First, while feeding the steel strip in the longitudinal direction, it was formed using forming rolls to obtain a U-shaped open pipe. A flux was supplied into the open tube through the opening of the open tube, and the opposing edges of the opening of the open tube were butt-welded to obtain a seamless tube.
This seamless tube was drawn to obtain a flux-cored wire with no slit-like gaps. However, some of the samples were pipes with slit-shaped gaps that were not seam-welded, and were drawn.
In this way, a flux-cored wire having a final wire diameter of φ1.2 mm was experimentally produced. In addition, during the drawing operation of these flux-cored wires, the flux-cored wires were annealed within a temperature range of 650 to 950° C. for 4 hours or more. After prototyping, a lubricant was applied to the wire surface. The composition of these flux-cored wires is shown in the table.

Tables 1A to 1E show rare earth oxide content, Cr content, fluoride content, F content, nitride content, N content, chemical composition (that is, fluoride, nitride , content of each element contained as chemical components excluding oxides and metal carbonates), content of specific oxides, content of specific fluorides, content of specific metal carbonates, and content of iron powder indicate. Note that the units of these contents shown in Tables 1A to 1E are % by mass with respect to the total mass of the flux-cored wire, except for the "amount of Ni in the outer sheath" shown in Table 1A. In the table, "mass% relative to the total mass of flux-cored wire" is abbreviated as "mass%", and "chemical composition excluding nitrides, oxides, fluorides, and metal carbonates" is abbreviated as "chemical composition". . In addition, the unit of "amount of Ni in outer skin" shown in Table 1A is % by mass with respect to the total mass of steel outer skin.

The F content shown in Table 1A indicates the amount of fluorine (F) contained in the fluorides in the flux in mass % with respect to the total mass of the flux-cored wire, and was determined by Equation B above. value (F conversion value).
The N content of the flux-cored wire shown in Table 1B indicates the amount of nitrogen (N) contained in the nitrides in the flux in mass % with respect to the total mass of the flux-cored wire, and is expressed by Equation A above. is a value (N-converted value) obtained by
The units for the amounts of Ni (Ni in flux, Ni in skin, Ni total) shown in Table 1C are all mass % with respect to the total mass of flux-cored wire.
The total specific oxides shown in Table 1D are Ti oxides, Fe oxides, Ba oxides, Na oxides, Si oxides, Zr oxides, Mg oxides, Al oxides, Mn oxides, K Total value of TiO ₂ , FeO, BaO, Na ₂ O, SiO ₂ , ZrO ₂ , MgO, Al ₂ O ₃ , MnO ₂ , K ₂ O or CaO conversion value of each content of oxide and Ca oxide is.

The remainder of the flux-cored wire shown in the table (ie, ingredients other than those shown in the table) is iron and impurities.
Among the flux-cored wires shown in the table, the flux-cored wires described as "seamless" in the "wire structure" column have a seamless shape and are used as lubricants unless otherwise specified in the "remarks" column. Wire coated with palm oil. In addition, the flux-cored wire described as "with slit-shaped gap" in the "wire structure" column is a wire having a slit-shaped gap, and the wire described as "perfluoropolyether coated" in the "remarks" column. is a wire coated with perfluoropolyether (PFPE) oil on its surface.
Each element listed in the Cr in the wire shown in Table 1A and in the chemical composition of the flux-cored wire shown in Table 1C is in the form of a steel skin or metal powder. In the table, numerical values outside the range defined in this disclosure are underlined.
In addition, in Tables 1A to 1E, blanks in the tables relating to the content of chemical compositions, compounds, etc. mean that the chemical compositions, compounds, etc. are not intentionally contained. These chemical compositions, compounds, etc. may be unavoidably mixed or produced.

[evaluation]
Evaluation was performed by gas-shielded arc welding using the flux-cored wires of Examples and Comparative Examples. Specifically, it was evaluated by the method described below.
A steel plate having a thickness of 50 mm and a tensile strength of 780 MPa class was used as the steel plate to be welded, and the type of welding gas used in the evaluation was Ar-20% CO ₂ gas. Also, in the evaluation, the welding current was all DC, and the polarity of the wire was all positive.
Welding conditions for evaluation were the conditions described in Tables 2, 3 and 4. The voltage was changed within a range of ±3 V depending on the arc state, and when the voltage was changed from the standard conditions (conditions shown in the table), the speed was adjusted so as to achieve the target heat input.

(Evaluation of slag entrainment)
Evaluation of slag entrainment was carried out by performing horizontal fillet welding on the steel plates described above under welding conditions E shown in Table 4. A flux-cored wire in which no slag was caught in all five cross-sections of the welded portion was evaluated as "acceptable".

(Evaluation of workability)
Bead-on welding was performed under welding conditions A, B and C shown in Table 2 to SM490 material having a thickness of 10 mm. The welding current is direct current, the type of welding gas and the polarity of the wire are as described above. The case where welding was possible under welding conditions A was rated as very good (⊚), the case where welding was possible under B was rated as good (∘), and the case where welding was possible or impossible under C was rated as poor (x).

(Evaluation of amount of spatter)
Downward bead-on-plate welding is performed on an SM490 material with a plate thickness of 10 mm under the welding conditions D shown in Table 3, and the spatter generated at that time is collected in a copper collection box installed around it, and the mass is measured. The amount of spatter generated per unit time (g/min) was measured. The welding current is direct current, the type of welding gas and the polarity of the wire are as described above. A spatter generation rate of less than 3.0 g/min was rated as very good (⊚), 3.0 g/min or more and less than 3.5 g/min was rated as good (∘), and 3.5 g/min or more was rated as poor (x).

(Evaluation of hot cracking resistance) T-shaped weld cracking test Evaluation of hot cracking resistance is performed on a steel plate with a thickness of 50 mm and a tensile strength of 780 MPa class under constant atmosphere control at a temperature of 20 ° C and a humidity of 60%. 4, and the welded joint obtained thereby was subjected to a test based on JIS Z 3153-1993 (T-shaped weld crack test method). The welding current is direct current, the type of welding gas and the polarity of the wire are as described above.
A flux-cored wire attached to a welded joint in which no cracks occurred in the T-shaped weld cracking test was evaluated as "acceptable" with respect to hot cracking resistance.

Table 5 shows the test results obtained by the method described above. In addition, when all the evaluation items were passed, the comprehensive judgment was passed, and when even one of the evaluation items did not pass, the comprehensive judgment was rejected.

It can be seen that when the flux-cored wires of the examples are used for welding, in gas-shielded arc welding, welding workability (especially vertical weldability) is high and hot cracking of the weld metal can be suppressed.
Furthermore, as shown in the test results in Table 5, the flux-cored wires of the examples were evaluated to be good in spatter amount and slag entrainment, and exhibited good welding workability.
Comparative Examples, on the other hand, did not meet any of the requirements specified in this disclosure and thus failed one or more of the evaluation criteria.

Claims (11)

A flux-cored wire for gas-shielded arc welding, comprising a steel sheath having a Ni content of 50% by mass or less and a flux filled inside the steel sheath, wherein the flux-cored wire is mass% relative to the total mass of the flux-cored wire. in a chemical composition containing 0.01 to 20.00% in total of rare earth oxides and excluding fluorides, nitrides, oxides, and metal carbonates, in mass% with respect to the total mass of the flux-cored wire, A flux-cored wire for gas-shielded arc welding having a Cr content of 0-22.00%. 2. The flux-cored wire according to claim 1, which contains fluoride and has an F content of 0.003 to 30.000% in mass % with respect to the total mass of the flux-cored wire. The flux-cored wire according to claim 1 or 2, which contains a nitride and has an N content of 0.003 to 15.00% in mass% with respect to the total mass of the flux-cored wire. The chemical composition, excluding fluorides, nitrides, oxides, and metal carbonates, in mass % relative to the total mass of the flux-cored wire,
C: 0.003 to 0.500%,
Si: 0 to 3.50%,
Mn: 0 to 10.00%,
P: 0 to 0.030%,
S: 0 to 0.030%,
Cu: 0 to 10.00%,
Ni: 0 to 50.00%,
Cr: 0-10.00%
Mo: 0 to 50.00%,
Nb: 0 to 0.500%,
V: 0 to 0.500%,
W: 0 to 10.00%,
Sn: 0 to 10.00%,
Sb: 0 to 10.00%,
Ti: 0 to 0.500%,
Al: 0 to 1.000%,
B: 0 to 1.000%,
Mg: 0-2.000%,
Ca: 0 to 2.000%,
REM: 0 to 0.5000%,
The flux-cored wire according to any one of claims 1 to 3, wherein Bi: 0 to 0.300% and the balance: Fe and impurities. selected from the group consisting of Ti oxide, Fe oxide, Ba oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, K oxide and Ca oxide containing one or more specific oxides, each of which is TiO ₂ , FeO, BaO, Na ₂ O, SiO ₂ , ZrO ₂ , The total content of the specific oxides is 10.00% or less in terms of MgO, Al ₂ O ₃ , MnO ₂ , K ₂ O or CaO, according to any one of claims 1 to 4. flux-cored wire. containing one or more specific metal carbonates selected from the group consisting of _{MgCO3 , Na2CO3} , _{LiCO3 , CaCO3 , K2CO3 ,} BaCO3, _FeCO3 , _MnCO3 and SrCO3 6. The flux-cored wire according to any one of claims 1 to 5, wherein the total content of the specific metal carbonate is 10.00% or less in mass % with respect to the total mass of the flux-cored wire. The flux-cored wire according to any one of claims 1 to 6, wherein the surface is coated with one or both of polytetrafluoroethylene oil and perfluoropolyether oil. The flux-cored wire according to any one of claims 1 to 7, wherein the total weight percentage of the rare earth oxide with respect to the total weight of the flux-cored wire exceeds 0.20%. The flux-cored wire according to any one of claims 1 to 8, wherein the Cr content is 0 to less than 10.00% in the chemical composition excluding fluorides, nitrides, oxides and metal carbonates. A method for manufacturing a welded joint, comprising a step of gas-shielded arc welding a steel material using the flux-cored wire according to any one of claims 1 to 9. 11. The method of manufacturing a welded joint according to claim 10, wherein in the step of gas-shielded arc welding, welding is performed using a torch that does not have a suction nozzle.